Multicast and broadcast transmissions currently are treated the same in many wireless networks. To date, similar treatment of these transmission types has not posed any substantial problems since wireless is a broadcast medium by definition and anyone on the same frequency with the appropriate receiver can receive the signal, irrespective of the destination. However, similar treatment of these transmission types is spectrally inefficient and, in some cases, these non-unicast transmissions may have a detrimental effect on power usage by a wireless device.
As an example, an access point or base station (both generally referred to as “AP”) has to make sure that a multicast transmission is sent at a modulation and coding rate that is acceptable to all wireless devices that are currently in communication with it. Therefore, for multicast transmissions, low (more robust and less efficient) transmission rates are commonly selected to accommodate each and every wireless device, even when a majority of the wireless devices can support significantly higher (less robust and more efficient) transmission rates.
Another disadvantage in supporting multicast transmissions for some wireless device is that, according to current IEEE 802.11 standards, there is no power-saving function to convert non-unicast (broadcast or multicast) transmissions to unicast transmissions while automatically adjusting the Delivery Traffic Indicator Map (DTIM). As a result, wireless devices may be required to “wake up” more often than needed to check for multicast or broadcast transmissions, which unnecessarily drains the battery of certain hand-held devices such as Voice-over-IP (VoIP) phones.